This invention relates generally to the control of machine tools and the like, and more particularly to a method and apparatus for monitoring and controlling a grinding process to optimize grinding productivity.
Although grinding processes possess a number of desirable features, including the ability to precision machine superalloys, they are difficult processes to control. The vibrational forces caused by the interaction of the grinding tool, i.e., wheel, and the workpiece are generally unstable and produce what is commonly referred to as regenerative chatter which grows or increases with time and eventually becomes unacceptable. Chatter is undesirable since it causes non-uniform relative motions between the workpiece and the grinding wheel at their interface and produces an undesirable non-uniform surface on the workpiece.
Although chatter is inevitable in a grinding process, chatter growth is a dynamic and complex phenomenon which is influenced by a number of factors such as the time-varying characteristics of the grinding machine and the cutting process, e.g., wheel loading. Therefore, the problem is not whether chatter will occur, but rather how it can be minimized and how the maximum allowable grinding time between dressings of the grinding wheel may be achieved. Because of the dynamic nature of the grinding process, it is impossible to set up fixed operating conditions which remain in a stable zone where chatter is minimized. Rather, in order to maintain optimum grinding conditions, it is necessary to monitor the grinding process and adaptively control the operating parameters. Although there have been a number of techniques proposed for accomplishing this, such as, for example, sensing the vibrations produced during grinding and varying the wheel loading in a predetermined manner in accordance with the vibrations, known techniques have not be entirely satisfactory. In part, this has been due to a rather poor understanding of the dynamic and complex nature of regenerative chatter.
It is desirable to afford a method and apparatus for dynamically monitoring and controlling a grinding process to minimize chatter and to maximize the allowable grinding time between dressings of the grinding tool. It is to this end that the present invention is directed.